A typical use of a power metal-oxide-semiconductor field-effect transistor (MOSFET) in an integrated circuit is in forming an electronic switch circuit. Two important characteristics of a MOSFET when used in a power switch circuit are its breakdown voltage and its ON resistance. The breakdown voltage is a measure of the MOSFET's ability to withstand voltage when it is in an OFF or open condition. The ON resistance is a measure of the resistance when the MOSFET is in an ON or closed condition. Improving the operation of a power switch circuit incorporating MOSFETs suggests using a MOSFET with a breakdown voltage as high as possible and an ON resistance as low as possible. A perfect switching device has an infinite breakdown voltage and zero ON resistance. Examples of high voltage semiconductor devices with relatively high breakdown voltages and relatively low ON resistances are disclosed in U.S. Pat. Nos. 4,823,173 and 5,264,719, which are herein incorporated by reference. It is desired in the art to have a MOSFET with further improved breakdown voltage and ON resistance.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a lateral DMOS structure with improved breakdown voltage and ON resistance.